There has been much research on the development of strong and safe polymer materials for special purposes. However, as discarded polymers have become socially recognized as a severe environmental problem all over the world, there is a need to develop an environmentally-friendly polymer material.
Environmentally friendly polymers may be mainly classified into photodegradable and biodegradable polymers. Biodegradable polymers have a functional group that can be decomposed by microorganisms.
Among these polymers, aliphatic polyester polymer has gained the most attention, since it has excellent workability and easily adjustable decomposition characteristics. In particular, polylactic acid (PLA) has a market share of about 150,000 tons in the world and expansively covers applications where common plastic is used, for example in food packaging materials and containers, cases for electronics, and the like. At present, polylactic acid resin is mainly used for disposable products such as food containers: wraps, films, and the like due to its biodegradable characteristics. Examples of polylactic acid resin are manufactured by American NatureWorks LLC., and Japan Toyota, and the like.
However, since a conventional polylactic acid resin lacks formability, mechanical strength, and heat resistance, a thin film made therefrom can be easily destroyed. Since it has low resistance against high temperatures, a molded product made therefrom can be distorted at 60° C. or higher.
Japanese Patent Laid-Open Publication Nos. 2006-131828 and 2006-199743 disclose a method for improving impact strength and heat resistance by using an impact-reinforcing agent or vinyl-based graft copolymer. However, the disclosed method is limited due to an increasing amount of polylactic acid, and particularly heat resistance may not be exhibited with a heavy load.
Japanese Patent Laid-Open Publication Nos. 2007-231149 and International Patent Laid-Open Publication No. 2006-097979 disclose a method for improving impact strength and heat resistance by using polymethylmethacrylate or an acrylic-based copolymer. However, this method may not realize high heat resistance because the acrylic-based copolymer itself has a lower heat resistance than polycarbonate and hinders crystallization of polylactic acid as well.